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Optimization of effective parameters on Reid vapor pressure (RVP) in an Iranian Condensate Stabilization plant and a Back-up unit

Arash Esamaeili a*

a

Islamic Azad University, Tehran-South Branch, Chemical Eng. Dept., Tehran, Iran Corresponding Author's E-mail: [email protected]

Keywords: Condensate stabilization, ASTM standards, RVP, HYSYS, Back-up unit Abstract Aim of this paper is to investigate RVP value in a condensate stabilization plant and a condensate Back-up unit which have located in Phases 6,7&8 Gas refinery (Assaluyeh, IRAN) with actual liquid flow rate of 82250 BPSD and obtaining best actual condition to operate them. On the basis of specified targets for stabilized condensate in these plants, two properties of product should be adjusted to store in storage tanks and export, first of all Reid vapor pressure (RVP) which is 10 Psia Max. (for summer case) and 12 Psia Max. (for winter case) according to ASTM D323 [1] that column pressure and re-boiler temperature are two key factors in it's adjustment , second amount of existence water that should be 500 ppmw in maximum case according to ASTM E203 [2]. The purpose of these plants is separation of aqueous phase and gaseous hydrocarbon from hydrocarbon condensate and then to stabilize it for export but only time that back-up unit is used is stabilization plant failure time. Our simulation by using HYSYS simulator (ver.2006) based on Peng-Robinson equation of state [3] indicates most suitable operating pressure for stabilizer and optimum temperature for re-boiler to achieve specified targets are 8.5 barg and 170°C respectively and also reflux flow rate for stabilizer column is almost 34.5 ton/hr so that these condition are now running in this plant, in this optimum case neither RVP is very low to lose more lighter hydrocarbons nor water content is very high. Ratio between Paraffins, Naphtenes and Aromatics in stabilization plant product is as P:N:A = 70.9: 22.01: 7.02. In comparison with back-up unit that doesn't have any distillation column and just uses heating and flushing processes, RVP value is much lower than stabilization plant, in this condition there is too much loss for light and heavy hydrocarbons. Results illustrate although light hydrocarbon (methane, ethane,...) values in product of back-up unit is much more than stabilization plant but due to loss a lot of paraffines and increase of naphtenes and aromatics in product of this unit, RVP value is lower so that ratio for this product is as P:N:A= 68.1: 22.4: 9.3. Tables 1 and 2 show simulated data by HYSYS which have good agreement with laboratory results. Table1: Data of boiling point curves for stabilization plant product based on ASTM standards Cut point(%) TBP (°C ) ASTM D86 (°C ) ASTM D1160 Atm. (°C ) ASTM D2887 (°C ) 0.0 -11.73 30.13 18.73 -11.96 1.0 -10.25 30.83 19.53 -10.14 2.0 -6.66 32.57 21.44 -8.56 5.0 1.87 37.04 25.83 -3.05 10.0 28.62 54.39 40.10 25.08 15.0 35.79 59.69 45.66 36.31 20.0 66.73 84.27 73.42 64.98 30.0 86.39 99.99 92.15 91.74 40.0 103.8 112.9 108.1 109.2 50.0 126.2 129.2 126.2 134.8 60.0 148.3 146.4 148.3 155.1 70.0 165.4 160.1 165.5 169.2 80.0 184.6 175.8 184.6 186.0 90.0 198.0 186.8 198.0 200.6 98.0 208.8 195.8 208.8 212.1 100.0 211.5 198.1 211.5 219.3

Table2: Properties of stabilized condensate based on optimum parameters and ASTM standards ASTM test Simulated values for Simulated values for Property method stabilization plant Back-up unit Reid vapor pressure (Psia) Water Content (ppmw) Pour point (°C ) Density @ condition P,T (Kg/m3 ) D323 E203 D97 D4052 8.91 nil -106.7 698.4 7.64 9.0 -96.4 704.7

Figure1: Process of simulated condensate stabilization plant in Phases 6,7&8 Gas Refinery

Figure2: Process of simulated condensate back-up unit in Phases 6,7&8 Gas Refinery Acknowledgement: The author thanks Phases 6,7&8 gas refinery laboratory for giving required data to investigate simulation results. References 1. ASTM D323-08: Standard Test Method for Vapor Pressure of Petroleum Products (Reid Method). 2. ASTM E203­08: Standard Test Method for Water Using Volumetric Karl Fischer Titration. 3. Peng, D.Y., Robinson, D.B., " A new two-constant equation of state". Ind. Eng. Chem. Fundam 15, 59-64, 1976. 4. ASTM D97 ­ 09: Standard Test Method for Pour Point of Petroleum Products.

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